Difference between Eubacteria and Archaebacteria

The prokaryotes have a very large group of unicellular organisms. Prokaryotes includes eubacteria and archaebacteria. They are similar in some features but are different in chemical composition.

Eubacteria and Archaebacteria are structurally similar but have different molecular characteristics.

Eubacteria

Eubacteria are unicellular organisms. They live in more neutral conditions. They can be found everywhere around us. Thousands of species of bacteria are differentiated based on morphology, chemical composition, nutritional requirements, biochemical activities and sources of energy. Eubacteria includes most of the commonly encountered bacterial forms (i.e. pathogenic bacteria and probiotic bacteria)

General Characters of Eubacteria:

1. Bacteria or Eubacteria are the prokaryotic organisms, lacking the nucleus and other membrane-bound organelles. So, all the process takes place in the cytoplasm.
2. The bacterial cell is enclosed in an envelope which protects, Supports and regulates transports of materials.
3. Bacteria contain single, circular chromosomes as their genetic material and ribosomes for the synthesis of the protein.
4. The cell wall is made of peptidoglycan, having ester linkage of Fatty acids.
5. They have the special appendages for the motility and can reproduce even under extreme condition by the formation of Spores.
6. They can reproduce sexually as well as asexually. They varied in their size and shape. Bacteria can be pathogens or non- pathogens.
7. Gram positive and Gram negative are the two types of bacteria.The differences in both are basically due to the cell wall and the Colour they give after the staining.
8. The Gram-positive bacteria show the positive result and appear purple when seen under a microscope. Staphylococcus, Bacillus, Streptococcus are the examples of Gram-positive bacteria.
9. On the other hand, the Gram-negative bacteria do not take up the crystal violet stain. Salmonella, Shigella, Pseudomonas are some of the examples.

Shape, size and arrangements of bacteria:

1. Bacteria are present in many sizes and several shapes. Most Bacteria range from 0.2 to 2 pm in diameter and 2 to 8 pm in Lengths.
2. There are few basic shapes of bacteria like spherical (coccus). Rod shape (bacillus), spiral shape etc.
3. Cocci are usually round but sometimes can be oval, elongated or flattened at one end. When cocci divide by binary fission, cells may remain attached to each other. Coco which remain in pair are called as diplococci. Some cocci divide and forms a chain known as Streptococci. Those cocci that divides into two planes and remain in group of four are known as tetrads. Those that divide in three planes and remain attached in a cube like group of eight are known as Sarcinae. Those that divide in multiple planes and form grape like structures are called as Staphylococci. These characteristics are helpful in identification of cocci.
4. Bacilli appears as single rod, diplobacilli are present in pair of streptobacilli occur in chains. Some bacilli are oval and look like elongated cocci and are known as coccobacilli.

Archaebacteria

Archaebacteria are the oldest living organisms on earth. They are prokaryotes and unicellular. They are found in very extreme conditions (such as at the bottom of the sea or in volcanic vents) in which others cannot live and carry out unusual metabolic processes.

General Characteristics of Archaebacteria:

1. Archaebacteria are the oldest living organisms on earth.
2. They are prokaryotes and unicellular with the undeveloped nucleus and lacks other organelles.
3. Archaea consist of the single-circular chromosome in the form of the plasmid.
4. Archaea size varies from 0.5-4 .
5. They are found in very extreme conditions and called extremophiles (such as at the bottom of the sea or in volcanic vents) in which others cannot live and carry out unusual metabolic processes.
6. tRNA (transferase RNA) have the leading role in decoding DNA and building proteins.
7. They possess different shapes like spirals, rods, plates and spheres, while some may be flat or square shaped also.
8. The cell wall of archaea is made up of pseudo peptidoglycans. The lipid membrane is ether linked, with the branching of aliphatic acids.
9. They divide asexually by budding, fragmentation or binary fission Process.
10. The outer cellular membrane act as the barrier to the cell and its outer environment is made up of phospholipid (pseudo peptidoglycans).
11. They also have the cell wall which is the outer layer of the cell and helps in maintaining the cell shape and the chemical equilibrium.
12. Inside the cell membrane is the cytoplasm where other cellular debris and the genetic material is placed.
13. Archaea divide asexually by the process of binary fission, Budding or fragmentation.
14. They have only one flagellum for their motility.
15. Methanogens, Sulphur dependent archaebacteria, Thermophiles ES and Halophiles are the four types of archaea.

Examples of Archaebacteria:

1. Methanogens: These are strict anaerobes that produce methane from carbon dioxide and hydrogen. They are the only form of life known to be able to perform cellular respiration using carbon as their electron acceptor. This gives them an important ecological niche because the breakdown of complex carbon compounds into the simple molecule of methane is the final step in the decomposition of most life forms. Without methanogens, the Earth’s carbon cycle would be impaired. Methanogen archaebacteria can be found in marshes and wetlands, where they are responsible for “swamp gas” and part of the marsh’s distinctive smell, and in the stomachs of ruminants such as cows, where they break down sugars found in grass that are undigestible to eukaryotes by themselves. Some methanogens live in the human gut and assist us in the same way. They can also be found in deep sea sediments, where they produce pockets of methane beneath the ocean floor e.g. Methanosarcina (Gram positive cocci in clusters). Methanobacterium. Gram positive long rod, Methanospirillum: Gram negative filamentous bacteria.
2. Halophiles (halos-salt, philes-loving): Archaebacteria that flourish in extremely saline environment are known as halophiles. These requires high salt concentrations about 17 to 23%. They can be found anywhere with concentration of salt five times greater than that of the ocean such as Great Salt Lake, Owens Lake, Dead Sea, etc. e.g. Dunaliellasalina, Halobacterium salinarum. Halophiles can tolerate high salt concentrations due to Presence of special lipid in the cell membranes, occurrence of mucilage covering, absence of sap vacuoles and hence plasmolysis is also absent, high internal salt content.
3. Sulphur dependent archaebacteria: Usually found in acidic hot springs. They are divided into two main types: the aerobic, sulfur- oxidizing e.g. Sulpholobus and the strictly anaerobic sulfur- reducing e.g. Thermoproteus.
4. Thermophiles: Archaebacteria that live in extremely hot temperatures are called thermophiles. They can grow and reproduce at temperature 100°C, and sometimes even above. Thermoacidophiles have dual ability to tolerate high temperature as well as high acidity due to branched chain lipids in the cell membranes. They often live in hot sulphur springs where the temperatures are as high as 80°C and pH as low as 2. They are chemosynthetic and obtain energy for synthesis of food from oxidizing sulphur. They are found in acidic soils, hot springs and near volcano openings.

BACTERIAL STRUCTURE